1. Field of the Invention
The present invention relates to a hale-machining method and an apparatus thereof for machining a workpiece by way of hauling or haling a tool on a surface of the workpiece, especially machining the workpiece by the tool in an attitude control in which a direction of a tool axis is substantially coincided with a normal direction of the machined surface of the workpiece and a front rake surface of the tool is substantially directed at a perpendicular angle to a feeding direction of the tool. This machining is called as the hale-machining hereinafter.
2. Description of the Related Art
It is well known for a high precision machining to machine a workpiece having three-dimension free curved surface, for example in “High Precision Free Form Surface Machine, Model AHN05 NanoProcessor” Tetsuro Shibukawa et. al., Toyoda Koki Technical Review, Vol. 43 No. 2 Page 61–65, published by TOYODA KOKI KABUSHIKI KAISHA Oct. 25, 2002. This NanoProcessor machine is described in the U.S. patent application Ser. No. 10/684,547 and in the European Patent Application No. 03 023 392.8. In this well known machine, a B-axis rotary table is mounted rotatably around a B-axis parallel to a Y-axis on a Y-axis slide table slidably mounted on a bed along the Y-axis. A tool is mounted on a tool base fixed on the B-axis rotary table. A workpiece table is slidably mounted on the bed along an X-axis and Z-axis directions each of which is perpendicular to the Y-axis. A workpiece spindle holding a workpiece is mounted on the workpiece table rotatably around C′-axis parallel to the Z-axis. Thereby, a tool axis direction of a tool is coincided with a substantial normal direction of a machined surface by rotating the rotary table and the spindle around the B-axis and C′-axis. In addition thereto, the workpiece table and the tool base are straightly moved along the X-axis, Y-axis and Z-axis directions relatively to machine a machined surface of the workpiece to a desired three dimensional free curved surface in high accuracy.
Recently, it becomes for a lens to be complex in a function and a shape, and there appears a lot of lens and die for the lens machined by hale-machining. As shown in FIG. 1, a tool axis direction L of a haling tool 34 is coincided with a normal direction N of machined surface WS of a workpiece and a front rake surface 34c of the haling tool 34 is substantially maintained in perpendicular to a feed direction F of hale-machining. Therefore, the attitude of the haling tool 34 is swung up and down by maintaining the tool axis to the normal direction and right and left by maintaining the front rake surface at the perpendicular angle to the cutting feed direction so that a removable amount is precisely maintained in constant. On the result, the machined surface of the workpiece W can be machined by haling tool 34 to achieve a high geometrical accuracy in the pre-determined three-dimensional free curved surface. However, the well-known high precision machine is not provided with mechanical means to swing or rotate right and left the workpiece or the haling tool around an A-axis parallel to the X-axis, therefore, the well-known precision machine can not hale-machine the machined surface of the workpiece in three-dimensional curved surface because the front rake surface of the haling tool can not be substantially maintained at the perpendicular angle to the cutting feed direction F at any time.
Although the well-known precision machine can hale-machine a two-dimensional surface of the workpiece by the haling tool, however, since the cutting point is far from a center of the C′-axis in cutting a peripheral portion on the workpiece, it is needed to provide an interpolation control in the C′-axis, the X-axis and the Y-axis so that it makes the controller complex. And also, the swing of the workpiece around the C′-axis is achieved by the workpiece spindle which performs another job of a continuous rotation, an error or deviation based on the continuous rotation affects the swing movement to deteriorate an accuracy in especially hale-machining the workpiece far from a center of the C′-axis.